1. Field of the Invention
The present invention relates to a thermal transfer laminate film, a thermal transfer sheet, and image-forming apparatus.
2. Description of the Related Art
In general, an image formed on photographic paper, such as an ink image formed by a sublimation dye transfer printing method using sublimation dye or thermal diffusion dye is coated with an image-protecting layer made of a thermoplastic resin to protect the ink image.
The coating of the image-protecting layer can be formed over the ink image by thermocompression using a heat roller, or by adhesion using an adhesive at room temperature.
For example, an image-laminating film is used. The image-laminating film includes a base film and an image-protecting layer formed of a thermoplastic resin on the base film. In use of the image-laminating film, the image-protecting layer of the image-laminating film is partially heated and pressed, so that only the image-protecting layer is transferred onto photographic paper. In this technique, a thermal transfer laminate film may be used (for example, Japanese Unexamined Patent Application Publication Nos. 59-76298, 59-85973, and 60-204397).
By use of a thermal transfer laminate film, images can be protected from gases that may degrade the images. A UV light-absorbable thermal transfer laminate film can prevent images from discoloring or fading. Also, the ink forming images is prevented from being transferred to other materials or articles containing a plasticizer, such as a plastic eraser. As described above, the use of a thermal transfer laminate film can provide various properties, such as plasticizer resistance, rubfastness and sebum resistance, to printed images.
Printed matter produced by coating an ink image with an image-protecting layer is used not only as merely image-printed matter, but also as an alternative to a silver halide photograph, such as an identification photograph.
In the thermal transfer method, only the image-protecting layer of a thermal transfer laminate film including a base film and a thermoplastic resin image-protecting layer is partially heated and pressed, so that only the heated image-protecting layer is transferred onto photographic paper. Accordingly, the materials of the thermal transfer laminate film are designed mainly so that the image-protecting layer and the base film can easily be separated. Value-adding properties or functions of printed matter, such as glossiness, have not yet been controlled.
A thermal transfer head has a structure in which heaters are continuously aligned in the principal scanning direction. The temperature of the heaters rises to 300° C. or more for printing. When thermal energy is transmitted in the thickness direction of the ink ribbon (particularly the thermal transfer laminate film) from the thermal transfer head, the layers of the thermal transfer laminate film and the receiving layer of the photographic paper have a temperature distribution according to the arrangement of the heaters of the thermal transfer head. The thermal transfer laminate film include a heat-resistant slip layer, the base film, an adhesion promoting layer or primer layer (optionally), a non-transferable release layer, the image-protecting layer, and an adhesive layer. When the resin materials of these layers come to a molten state, the same temperature distribution arises.
Consequently, the ink ribbon is cooled from a high temperature of 300° C. or more after scanning the thermal transfer head. Since the base film of the ink ribbon is thermally deformed (shrunk) during cooling, the interface between the non-transferable release layer and the image-protecting layer is also deformed concurrently. Consequently, the ink ribbon is peeled at the interface between the non-transferable release layer and the image-protecting layer to make the surface of the image-protecting layer rough and expose the rough surface. Light incident on such a rough surface of printed matter is scattered to degrade the glossiness of the surface of the printed matter undesirably.
In order to solve the problem that the rough surface of the image-protecting layer of printed matter causes light scattering to degrade the glossiness, the following measures have been taken.
One of the measures is that a secondary pressure is applied to printed matter whose ink is coated with an image-protecting layer thermally transferred from a thermal transfer laminate film by a roller having a smooth surface of 25 μm or less in surface roughness, thus giving glossiness to the surface of the printed matter (for example, Japanese Unexamined Patent Application Publication No. 63-209993).
In another measure, a pressuring surface is provided to the downstream side of the heaters of the thermal transfer head, and a smooth surface is formed by pressurization with the flat pressuring surface (for example, Japanese Unexamined Patent Application Publication No. 2005-125747).
These two measures enhance the glossiness by surface treatment of the printed matter.
A polyester film is proposed for a sublimation dye transfer ribbon (for example, Japanese Unexamined Patent Application Publication No. 2007-160768). This film maintains the anisotropy of glossiness at the surface of the image-protecting layer after transfer and also maintains high glossiness.
The above cited measures however apply secondary treatment to the printed matter, and accordingly, the system of the sublimation-type printer becomes excessively large. In addition, for example, extra materials are used for the secondary treatment. Thus, these measures are disadvantageous in cost. Furthermore, a glossiness at the same level as silver halide photographs is not sufficiently obtained only by smoothing the base film.
In another measure, a cushion layer is provided between the support and the thermal transfer layer of a thermal transfer material (for example, Japanese Unexamined Patent Application Publication No. 2001-162937). When an image is formed with a metallic glossy coloring material having a single hue, the cushion layer is used to bury the particles of the metallic glossy coloring material.